Stack for producing forced draft



Dec. 27, 1932. WOLF 1,892,417

- v STACK FOR PRODUCING FORGED DRAFT Filed Oct. 22. 1931 Patented Dec. 27, 1932 I UNITED sTATEs e-ATEN oFFi-cE.

KowAnn ivr. WOLF, or rumors, INDIANA, ASSIGNOZR. fro THE BRODERICK oorrrANY,

A CORPORATION OF INDIANA STACK r03 raonuomeroncnn DRAFT Large, portable boilers of the type commonly used in oil fields, for example, must often develop power very much greater than their rated capacities. Thus, a boiler rated at one hundred and twenty-five horse power must frequently develop four hundred horse power. It has heretofore been the practice to provide one hundred and twenty-five horse powerboilers with stacks about thirty inches in diameter and thirty-five feet long. Such a stack weighs fourteen hundred pounds or more, and considerable work is required to set up and anchor the stack whenever the boiler is moved, quite apart from the work involved in moving the stack. Even with these large stacks, when the boilers are pushed far above their rated capacities, a forced draft is required. The usual method of effecting the forced draft is to blow steam under a pressure of from 190 pounds to 250 pounds into the stack through a three-quarter inch or an inch pipe, thereby consuming from twenty-five per cent to thirtyper cent of the steam generated by the boiler.

The object of the present invention is to make it possible to operate boilers with comparatively small, light stacks and to blow these stacks, to induce a strong forced draft, with only a small fraction of the steam heretofore needed for that purpose.

In carrying out myinventionI employ a small jet of steam which is made to combine with the combustion gases to produce a larger jet which carries the combustion gases out of the stack and at the same time so reduces the that carries steam or other gaseous fluid under high pressure, discharges a jet upwardly into the lower end of the small inner Venturi tube, at a point below the contracted part in the latter. This steam, under high pressure and of low volume, enters the inner Venturi tube at high velocity, causing a partial vacuum in the lower end of this'Venturi tube whereby combustion gases are driven into thelower end of the inner Venturi tube,-mix with the steam, and are carried upwardly; The inner Venturi tube increases gradually is crosssectional area from the contracted portion toward the top. Therefore the velocity of the gaseous mixture decreases as it rises in the inner tube, and the mixture spread'sout into a larger space. Therefore,as the gaseous mixturerreachesthe upper end ofthe inner Venturi tube, the volume thereof vis relatively large and the pressure and velocity are moderately low.

In other words, a small jet, under'high pressure, and at high velocity enters the lower end of the inner Venturi tube which then delivers into'the contracted portion of thestack a large jet under relatively low pressure and; moving at a relatively .low speed. This large, slowly moving jet creates apartial vacuum in the lower portion of the stack, in thespace surrounding the inner Venturitube, and causes the gases in this space to be drawn up and discharged out of the top of the stack.

By constructing thestacks in accordance with my invention, I find that they need not be more than eightfeet long instead of thirty-five feet long, as heretofore, and need not weight more than about three hundred pounds. So far as the'consumption of steam to produce the draft is concerned, I find that there is inmany cases less than one-fifth of that heretofore used, averaging less than siX per cent of the steam generated.

The various features of novelty whereby my invention is characterized will herein after be pointed out with particularity in the claims; but, for a'full understanding of my invention and of itsobjectsjand advantages, reference maybe had to the following detailed description taken in connection with the accompanying drawing, wherein:

Figure 1 is a view, partly in elevation and partly in section, showing a fragment of a boiler having one of my improved'stacks; and Fig. 2 is a top plan view of the stack.

.Referring to the drawings, 1 and 2 represent frustoconical shells, arranged in axial alignment with each other, the large end of the lower shell being at the bottom and the large end of the upper shell being at the top;

and there being a short cylindrical shell 3 connecting the shells 1 and 2 and constituting the contracted neck of the .Venturi tube formed by the three shells. This Venturi tube takes the place of the usual stack rising from a boilert orsmoke chamber associated with the boiler. r

In the lower half of the stack is a second Venturi tube of comparatively sma-lldiameter. In thearrangement shown, this second or inner Venturi tube consists of a short lower section in the form of a bell 5 and a long uppersection-G openingout of the top of the bell and increasing gradually in diameter toward the upper. end. The diameter of the open bottom of the bell is much greater than the diameter of the lower end of the tubular section 6, so that the juncture of the bell and the section 6 forms the contracted neck of the inner Venturi tube. The inner Venturi tube is coaxial with the stack and its upper end lies just below the contracted portion or neck of the outer Venturi tube or stack.

The inner Venturi tube may be supported in fixed relation to the stack in any suitable way. In the arrangement shown, the inner tube has near its upper end a plurality of radial arms 7 projecting therefrom and welded or otherwise secured at their outer ends to the surrounding stack wall.

Extending up into thebottom of the'bell 5 a short distance is a small pipe 8 so positioned that fluids discharged therefrom will be delivered in the upward direction along the long axis of the inner Venturi tube. In actual practice this pipe may be an ordinary quarter-inch pipe. When steam at a pressure of from one hundred ninety pounds to two hundred and fifty pounds per square inch is discharged from this pipe at high velocity, it creates a partial vacuum in the bell, causing combustion gases or smoke to enter the bell and mix with the steam. As the mixture rises itspreads laterally within the enlargingtube,

and the velocity and pressure decreases. The mixture issues from the upper end of the inner Venturi tube in the form of a' jet of large volume at a velocity and pressure that are lower compared with the velocity and pressure of the steam jet. This large, secondary jet creates a partial vacuum in the space 9 within the stack and surrounding the inner Venturi tube which induces the necessary draft in thecoinbustion chamber of the plant.

lVhile'I have illustrated and described with particularity only a single preferred form of my invention. I do not desire to be limited to the exact structural details thus illustrated and described; but intend to cover all forms 65 and arrangements which come within the definitions of my invention constituting the appended claims.

I claim:

1. In combination, a smoke stack in the form of a Venturi tube, a second, inner Venturi tube smaller in cross-sectional area than the stack fixed within and coaxial with the stack, said inner Venturi tube consisting of a long upper section tapering only slightly from the smaller end toward the top and a short flaring lower section or bell, the upper end of the inner Venturi tube being positioned in the vicinity of the contracted part of the stack and the lower end of the inner Venturi tube opening out into the stack, and means to produce within theinner tube and below the contracted part thereof an upwardly-directed jet.

2. In combination, a smoke stack in the form of a Venturi tube, a second, inner Venturi tube fixed within and coaxial with the stack, tlie upper end of the inner Venturi tube being positioned in the vicinity of the contracted part of the stack, said inner Venturi tube consisting of a long upper section the diameterof whose upper end is much smaller than the diameter of the contracted part of the stack and a short flaring lower section or hell opening out into the stack and having a diameter which is only a small fraction of the diameter of thesurrounding part of the stack. and a steam pipe of small diameter coaxial with the inner Venturi tube extending up into the lower end of the latter and having an open upper end positioned below the contracted part of the inner Venturi tube.

In testimony whereof, I sign this specification.

HOlVARD M. WOLF. 

